Helicobacter pylori bacterial infections are a serious problem in humans. They have been shown to be a strong causative factor in gastric ulcer disease, such as stomach ulcers and small intestine ulcers which can result in death. Helicobacter pylori is a gram-negative, S-shaped, microaerophilic bacterium that was discovered and cultured from a human gastric biopsy specimen. (Warren, J. R. and B. Marshall, (1983) Lancet 1: 1273-1275; and Marshall et al., (1984) Microbios Lett. 25: 83-88). H. pylori bacterial cells can survive in a low pH environment because of an enzyme on their outer cell wall called urease. Urease converts urea in the stomach into bicarbonate and ammonia. The bicarbonate and anunonia neutralize the acid gastric juices, thereby providing a protective layer around the H. pylori.
Since H. pylori are gram-negative rod type bacteria, it is difficult to treat H. pylori infections without using agents that will also affect other gram-negative bacteria elsewhere in the body. H. pylori has been strongly linked to chronic gastritis and duodenal ulcer disease. (Rathbone et. al., (1986) Gut 27: 635-641). Moreover, evidence is accumulating for an etiologic role of H. pylori in nonulcer dyspepsia, gastric ulcer disease, and gastric adenocarcinoma. (Blaser M. J., (1993) Trends Microbiol. 1: 255-260). Transmission of the bacteria occurs via the oral route, and the risk of infection increases with age. (Taylor, D. N. and M. J. Blaser, (1991) Epidemiol. Rev 13: 42-50). H. pylori colonizes the human gastric mucosa, establishing an infection that usually persists for decades. Infection by H. pylori is prevalent worldwide. Developed countries have infection rates over 50% of the adult population, while developing countries have infection rates reaching 90% of the adults over the age of 20. (Hopkins R. J. and J. G. Morris (1994) Am. J. Med. 97: 265-277).
The bacterial factors necessary for colonization of the gastric environment, and for virulence of this pathogen, are poorly understood. Examples of the putative virulence factors include the following: urease, an enzyme that may play a role in neutralizing gastric acid pH (Eaton et al., (1991) Infect. Immunol. 59: 2470-2475; Ferrero, R. L. and A. Lee (1991) Microb. Ecol. Hlth. Dis. 4: 121-134; Labigne et al., (1991) J. Bacteriol. 173: 1920-1931); the bacterial flagellar proteins responsible for motility across the mucous layer (Hazell et al., (1986) J. Inf. Dis. 153: 658-663; Leying et al., (1992) Mol. Microbiol. 6: 2863-2874; and Haas et al., (1993) Mol. Microbiol.8: 753-760; Vac A), a bacterial toxin that induces the formation of intacellular vacuoles in epithelial cells (Schmitt, W. and R. Haas, (1994) Molecular Microbiol. 12(2): 307-319) and several gastric tissue-specific adhesions (Boren et al., (1993) Science 262: 1892-1895; Evans et al., (1993) J. Bacteriol. 175: 674-683; and Falk et al., (1993) Proc. Natl. Acad. Sci. USA 90: 2035-2039).
Certain therapeutic agents are known to eradicate H. pylori infections in vitro. (Huesca et. al., (1993) Zbl. Bakt. 280: 244-252; Hopkins, R. J. and J. G. Morris, supra). However, many agents are suboptimally effective in vivo because of bacterial resistance, altered drug distribution, patient non-compliance, poor drug availability and lack of selectivity for H. pylori. (Hopkins, R. J. and J. G. Morris, supra). Treatment with antibiotics combined with bismuth are part of a standard regime used to treat H. pylori infection. (Malfertheiner, P. and J. E. Dominguez-Munoz (1993) Clinical Therapeutics 15 Supp. B: 37-48). Recently, combinations of a proton pump inhibitor and a single antibiotic have been shown to ameliorate duodenal ulcer disease. (Malfertheiner, P. and J. E. Dominguez-Munoz supra).